1. Field of the Invention
The present invention relates to an optical illumination device, an exposure device, and an exposure method, and more particularly to an optical illumination device suitable for an exposure device for fabricating, by means of a lithographic process, microdevices such as a semiconductor element, an image pickup element, a liquid crystal display element, and a thin-film magnetic head.
2. Related Background Art
In a typical exposure device of this kind, the light beam (radiation beam) emitted by the light source enters a fly's eye lens such that a secondary light source comprising a multiplicity of light sources is formed on the back focal plane of this lens. The light beam from the secondary light source enters a condenser lens (a condenser optical system) after being restricted via an aperture diaphragm disposed in the vicinity of the back focal plane of the fly's eye lens. This aperture diaphragm restricts the shape or size of the secondary light source to the desired shape or size in accordance with the desired illumination conditions (exposure conditions).
The light beam which is condensed by the condenser lens illuminates, by way of superposition, a mask formed with a predetermined pattern. The light transmitted by the pattern of the mask forms an image on a wafer via an optical projection system. The mask pattern is thus projection-exposed (transferred) onto the wafer. The pattern formed on the mask is highly integrated. A uniform illuminance distribution on the wafer is indispensable in order to accurately transfer the detailed pattern onto the wafer.
In an exposure device that has the constitution described above, there is a need to increase the fill of a multiplicity of light sources that constitute a secondary light source formed on the illuminated pupil plane in order to improve the image formation capacity.